The objective of the proposed research is to determine the public health importance of the presence of Echinococcus multilocularis, the etiologic agent of alveolar hydatid disease, in the northcentral United States where it is known to be endemic in wild mammals and the domestic cat. It is proposed that this objective can largely be realized by: (1) ascertaining the prevalence of the parasite in domestic cats and dogs through examination of large numbers of these animals from the endemic region; (2) determining if these domestic carnivores are important sources of human infection through the use of immunodiagnostic tests on persons known to have been closely associated with infected pets; (3) examining library and autopsy records of hospitals in the endemic region to determine if there have been autochthonous human cases which have not been published in the literature; and (4) examining numerous red foxes and coyotes from outside the endemic region to ascertain if E. multilocularis is widening its known geographic range. BIBLIOGRAPHIC REFERENCES: Kritsky, D. C., and P. D. Leiby. 1975. Comparison of yearly prevalences of Echinococcus multilocularis, Leuckart 1863 in Peromyscus maniculatus and Microtus pennsylvanicus in North Dakota. J. Parasit. 61: 1112-1113. Kritsky, D. C., and P. D. Leiby. 1975. Prevalence of Echinococcus multilocularis in domestic carnivores in North Dakota. J. Parasit. Abstract #46, 50th Ann. Meet. Am. Soc. Parasit., New Orleans, Louisiana, Nov. 10-14, 1975.